1. Field of the Invention
This invention relates to filter adjustment apparatus and to a method for adjusting cut-off frequencies, peak frequencies, or dip frequencies, for example, of a filter provided in an integrated circuit (IC).
2. Description of the Prior Art
In a check process for electronic circuits in general, it may become necessary to adjust the peak frequency, dip frequency or the cut-off frequency of the filter circuit to a prescribed target value. Above all, in a circuit formed in an analog integrated circuit or analog IC, while the circuit elements such as transistors, resistors or capacitors can be fabricated with a highly accurate relative ratio of the rated values thereof, the absolute values or magnitudes of these rated values vary from circuit to circuit. Hence, the aforementioned adjustment is thought to be indispensable in the filter circuit wherein a demand is raised for high accuracy.
In the conventional filter adjustment, it is usual to detect a filter output while consecutively changing or sweeping the frequency of an input signal to a filter so as to adjust peak or dip frequencies of a filter characteristic curve or cut-off frequencies to a prescribed value. In such case, the obtained characteristic curve is observed artificially to determine the cut-off frequencies or the peak or dip frequencies. Then, a filter adjustment is executed manually such that the frequencies reach the prescribed target value.
In the event of automating such filter adjustment, it should be noted that a difficulty arises for mechanically discriminating and reading said peak, dip or a cut-off points, which sometimes result in a lowered adjustment accuracy. Moreover, the structure for sweeping frequencies of an input signal becomes complicated. It is troublesome enough to repeat such sweeping while gradually changing the filter characteristics, spending considerable time for adjustment.